JPH10261238A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep compatibility with respect to disks whose substrate thickness are different without using an aperture or the like. SOLUTION: The optical characteristic of an objective lens is optimally designed with respect to a high-density disk whose substrate thickness is thick and a reflected light is diffracted by a hologram 11 to be received with a light receiving means 20. Then, the light receiving means 20 is constituted of a positive order light receiving part 21 receiving positive order diffracted light beams of a reflected light from a standard-density disk whose substrate thickness is thin and a negative order light receiving part 22 receiving the 1-st order diffracted light of a reflected light from the high-density disk and a central light receiving area having the size of the central part of the reflected light from the standard-density disk in which the influence of a spherical aberration is small is constituted of areas 21b-21d. Thus, the reproduced signal of the high-density disk and the reproduced signal of the standard-density disk are respectively calculated by a photoelectrically converted signal from the negative order light receiving part 22 and photoelectrically converted signals from the central light receiving area of the positive order light receiving part 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup device capable of maintaining compatibility with information recording media having different substrate thicknesses.

[0002]

2. Description of the Related Art Conventionally, a laser beam is condensed by an objective lens to form a laser spot, and the laser spot is applied to a recording member of an information recording medium (hereinafter, referred to as a disk) to form a mark (pit). 2. Description of the Related Art There is known an optical pickup device which forms and records information, and receives reflected light from a recording member to reproduce information recorded on the recording member. In the following description, an area where a mark exists is called a mark area, and an area between the mark areas is called a space area.

In response to recent demands for higher-density information, a high-recording-density disk called a so-called DVD has been developed as the above-mentioned disk.

Such a disk has a structure in which a recording member is sandwiched between transparent members such as plastics. The thickness of a transparent member to which laser light is irradiated (this transparent member is particularly referred to as a transparent substrate) has a thickness. The diameter is 1.2 mm for a disk having a conventional recording density, and 0.6 mm for a DVD.

In this specification, a disk having a conventional recording density is called a standard density disk, and a disk having a higher recording density than the standard density disk is called a high density disk. When you don't need to do that, you simply call it a disk. Therefore, the high density disk is D
Although not limited to VD, this will be described as an example in the following description.

With the development of such high recording density disks,
From the viewpoint of increasing the added value of the optical pickup device, it is desired that information can be recorded or reproduced on disks having different thicknesses of the transparent substrate.

In order to properly reproduce the information recorded on the recording member, it is necessary to converge the laser spot diameter to about 1.5 μm for a standard density disc and about 0.95 μm for a high density disc. Since the laser spot diameter is determined by the optical characteristics of the objective lens and the transparent substrate, when laser light of the same wavelength is focused on disks with different transparent substrate thicknesses using the same objective lens, the focused laser light The spherical aberration in the peripheral portion becomes large, and the peripheral portion in which the spherical aberration becomes large does not focus on the recording member surface. For this reason, it has been pointed out that the compatibility between the standard density disk and the high density disk cannot be maintained.

Therefore, an objective lens is optimally designed to minimize spherical aberration for a high-density disk having a thin transparent substrate, and a laser beam incident on the objective lens is applied to a standard-density disk having a thick transparent substrate. An optical pickup device has been proposed in which the peripheral portion of the optical pickup is shielded using an aperture or the like.

This problem will be described with reference to the drawings. FIG.
FIG. 11A is a diagram showing a focusing state when a laser beam is focused using an objective lens whose optical characteristics are optimally designed for a high-density disc. FIG.
1 (b) shows the case of the standard density disk LD.

As can be seen from FIG. 11A, when the optical characteristics of the objective lens are optimally designed for the high-density disk HD, all the laser beams L condensed by the objective lens are recorded. Focusing can be performed on the surface of the member M. However, when such an objective lens is used for a standard density disk LD, the peripheral portion of the laser beam L is not focused and substantially at the center as shown in FIG. Only the part is in focus.

That is, the portion near the optical axis of the laser beam L can be favorably focused on the surface of the recording member M, but the peripheral portion of the laser beam L has a large spherical aberration due to the large spherical aberration. The focus cannot be focused upward, and the peripheral portion becomes blurred.

Here, for a high-density disc, the light-collecting characteristics are optimized for all rays within the effective diameter of the objective lens. Even if the light rays of the part are well condensed (even if they are optimized), it is impossible to optimize the entire effective diameter of the objective lens including the outer peripheral part. No. "

FIGS. 12A and 12B are schematic diagrams showing the light intensity distribution of the reflected light when the laser light is satisfactorily focused on the surface of the recording member. Is shown. FIG. 12A shows the light intensity distribution of the reflected light when the laser light L is applied to the space area.
(B) shows the light intensity distribution of the reflected light when the mark area is irradiated with the laser light L.

As can be seen from FIG. 1, a portion Ia having a high light intensity exists in an "island" around the periphery of the reflected light from the space area. On the other hand, there is no such a portion with high light intensity around the reflected light from the mark area.

The light intensity distribution of the reflected light from the space area and the mark area can be divided by a predetermined circle Ib.
It is possible to identify a region where an island region exists by b, and a region with high light intensity by the circle Ib in the reflected light from the mark region.

When the laser spot scans the track in such a situation, the signal intensity of the reflected light becomes as shown in FIG.
As in the curve Ic. For comparison, the signal intensity when the peripheral portion of the laser beam incident on the objective lens is shielded by an aperture described later is shown as a curve Id.

The signal strength shows a change that shows a minimum value at the center of the mark. Therefore, for example, if a threshold value is appropriately set, it is possible to discriminate between the mark area and the space area based on whether the signal intensity exceeds the threshold value. In this case, in order to accurately or clearly distinguish between the mark area and the space area, it is required that the change amount D of the signal strength is large.

However, when the spherical aberration at the peripheral portion of the laser spot becomes large and an unfocused portion is formed on the surface of the recording member M and the laser spot diameter becomes large, the central portion of the laser spot moves to the central portion of the mark area. Even when irradiating,
A situation occurs in which the peripheral portion of the laser spot irradiates the space area, and it becomes difficult to increase the variation D of the signal intensity.

To solve such a problem, the peripheral portion of the laser spot incident on the objective lens is shielded by the aperture so that the laser spot condensed by the objective lens does not include a peripheral portion having a large spherical aberration. A method has been proposed in which all the laser beams incident on a disc can be focused (for example, JSAP Preliminary Proceedings, Fall 1995, 29a-ZA-6, "Compatibility between two types of discs having different thicknesses"). Examination of gender ”).

[0020]

However, when the optical characteristics of at least the objective lens are optimally designed for one disk, an aperture is not required when recording and reproducing the disk. Therefore, it is necessary to move the aperture in and out of the optical path according to the type of the disk. For example, when the optical characteristics of the objective lens are optimally designed for the high-density disc HD, the aperture is retracted from the optical path when reproducing the high-density disc HD, and the aperture is used when reproducing the standard-density disc LD. It must be inserted in the optical path.

For this reason, a mechanism for inserting and removing the aperture is required separately, and a high precision is required for the positional accuracy of the insertion position of the aperture, and a high precision is also required for parts and assembly of the aperture removing mechanism. Since it is required, there is a problem that productivity of the optical pickup device is reduced and cost is increased.

Accordingly, the present invention is to separate a peripheral portion, which is largely affected by spherical aberration in reflected light, from a central portion so as to be able to receive light without using an aperture, and to detect a high-quality signal which is less affected by spherical aberration. It is an object to provide a possible optical pickup device.

[0023]

According to the first aspect of the present invention, there is provided a laser generating means for emitting a laser beam to an information recording medium having a transparent substrate having a different substrate thickness, and an optical characteristic for at least one of the information recording mediums. In an optical pickup device which is optimally designed and has an objective lens for condensing incident laser light and a light receiving means for receiving reflected light from an information recording medium and outputting a reproduction signal and a servo signal, the light receiving means comprises: It is characterized by having a central light receiving area for receiving a central portion where the influence of spherical aberration on reflected light from an information recording medium for which optical characteristics of the objective lens is not optimally designed is small.

That is, when the optical characteristics of the objective lens are optimally designed for one of the information recording media having different substrate thicknesses,
Since the reflected light from the other information recording medium includes a peripheral portion which is greatly affected by spherical aberration, a central light receiving area for receiving only reflected light other than the peripheral portion is formed in the light receiving means. .

According to a second aspect of the present invention, the grating is formed uniformly, and the incident reflected light is reflected by ± nth order (n =
0, 1,...) Diffracting means for diffracting the diffracted light at different angles, the light receiving means receiving a positive order light receiving section for receiving the + order diffracted light by the diffracting means, and receiving the negative order diffracted light. And a negative order light receiving section, which is arranged in a direction orthogonal to the grating direction formed on the diffraction means, and a central light receiving area is formed in one of the positive or negative order light receiving section. And

That is, the diffracting means converts the reflected light into ± n orders (n =
0, 1,...), And the + order diffracted light and the − order diffracted light are diffracted in opposite directions around the 0 order light, so that the + order diffracted light is received. A light receiving means is formed by a positive order light receiving unit for receiving the negative order diffracted light and a negative order light receiving unit for receiving the negative order diffracted light. Then, for example, the diffracted light in the reflected light from the information recording medium having a small substrate thickness is received by the positive-order light receiving portion, and the diffracted light in the reflected light from the information recording medium having the thick substrate is received by the negative-order light receiving portion. And a central light receiving area is formed in at least one of the positive and negative order light receiving sections.

According to a third aspect of the present invention, a light receiving center region is formed at a substantially central portion of each of the positive and negative order light receiving portions, one of which forms a central light receiving region and two light receiving centers. At least one of the regions is divided into two, and a tracking signal is detected based on a difference between photoelectric conversion signals from each of the divided regions.

That is, a light receiving center region is formed substantially at the center of the positive and negative order light receiving portions. At this time, one of the positive or negative order light receiving sections is set as the central light receiving area. Then, the light receiving central area of the positive and negative order light receiving sections is divided into two in a direction orthogonal to the direction in which the reflected light moves on the light receiving surface by tracking, for example, and the photoelectric conversion signal from the divided light receiving central area is divided. A tracking signal is detected based on the difference.

According to a fourth aspect of the present invention, a light receiving center region is formed at a substantially central portion of each of the positive and negative order light receiving portions, one of which forms a central light receiving region and two light receiving centers. At least one of the regions is divided into two, one of which
One is further divided into two in the direction perpendicular to the direction of the two divisions, and a tracking signal is detected based on a difference between photoelectric conversion signals from each of the further divided regions.

That is, a light receiving center region is formed substantially at the center of the positive and negative order light receiving portions. At this time, one of the positive or negative order light receiving sections is set as the central light receiving area. Then, the light receiving center area of the positive and negative order light receiving units is divided into two in the direction in which the reflected light on the light receiving surface moves by, for example, tracking,
Further, one of them is divided into two by tracking in a direction orthogonal to the direction in which the reflected light on the light receiving surface moves. A tracking signal is detected based on a difference between photoelectric conversion signals from a region divided into two in a direction orthogonal to a direction in which reflected light on the light receiving surface moves by tracking.

According to a fifth aspect of the present invention, when a reproduced signal is detected from a diffracted light in a reflected light from an information recording medium in which an optical characteristic of an objective lens is optimally designed, the central light receiving region and the central light receiving region are detected. When the detection is performed based on the photoelectric conversion signal from the surrounding light receiving peripheral area formed and the reproduced signal is detected from the diffracted light of the reflected light from the information recording medium for which the optical characteristics of the objective lens are not optimally designed, the center is used. The detection is performed by a photoelectric conversion signal from the light receiving area.

That is, when a reproduced signal is detected from the diffracted light in the reflected light from the information recording medium in which the optical characteristics of the objective lens are optimally designed, the central light receiving area and the light receiving formed around the central light receiving area are detected. When the reproduction signal is detected from the diffracted light in the reflected light from the information recording medium for which the optical characteristics of the objective lens are detected by the photoelectric conversion signal from the surrounding area and the optical characteristics of the objective lens are not optimally designed, The reproduced signal is detected only from the positive or negative order light receiving section in which the central light receiving area is formed by detecting the converted signal.

According to a sixth aspect of the present invention, a light receiving center region is formed substantially at the center of each of the positive and negative order light receiving portions.
One of them forms a central light receiving area, and these two light receiving central areas are divided in the grating direction.

That is, a light receiving center area is formed at substantially the center of each of the positive and negative order light receiving sections, one of which forms a central light receiving area, and the light receiving central area forming the central light receiving area is an object. Only the central part where the influence of spherical aberration on the reflected light from the information recording medium for which the optical characteristics of the lens is not optimally designed is small is received, and the other light receiving central region is from the information recording medium for which the optical characteristics of the objective lens are optimally designed. All reflected light is received. Also, for example, when the wavelength of the laser light emitted from the laser generating means changes due to a temperature change,
Since the diffraction angle of the diffracted light changes in a plane perpendicular to the grating direction, a dividing line is formed in each light receiving center area in a direction perpendicular to the grating direction, and the light is divided.
Thereby, even if the diffraction angle changes, the diffracted light is prevented from deviating from the corresponding light receiving area.

According to a seventh aspect of the present invention, the light receiving peripheral region is formed doubly around the central light receiving region, and the central light receiving region and the two peripheral light receiving regions are divided into two. Features.

That is, the surrounding light receiving region is formed doubly around the central light receiving region formed in the light receiving means, and the central light receiving region and the two surrounding light receiving regions are divided into two. When a reproduced signal is detected from the diffracted light in the reflected light from the information recording medium in which the optical characteristics of the objective lens are optimally designed, the detected signal is detected from the photoelectric conversion signals from the two ambient light receiving areas and the central light receiving area. When the reproduction signal is detected from the diffracted light of the reflected light from the information recording medium whose optical characteristics of the objective lens are not optimally designed, it is detected by the photoelectric conversion signal from the central light receiving area. .

The invention according to claim 8 is characterized in that the laser generating means and the light receiving means are unitized.

That is, the laser generating means and the light receiving means are
It is characterized by being housed in one can and unitized.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical system in an optical pickup device according to the present invention.

The optical pickup device comprises a laser generating means 1 for emitting laser light, a collimating lens 2 for converging the laser light from the laser generating means 1 into substantially parallel light,
A beam splitter 3 that allows the laser beam from the collimating lens 2 to pass and deflects the reflected light from the disk. Optimal optical characteristics of the high-density disk HD are designed so that the aberration is reduced for a predetermined numerical aperture. Then, an objective lens 5 for condensing the incident laser light, a detection lens 10 for converging the reflected light, a hologram 11 for diffracting the reflected light converged by the detection lens 10, a tracking signal for receiving the diffracted light, and a focus signal It has a light receiving means 20 for outputting a signal and a reproduction signal.

Although not shown, a configuration in which the collimator lens and the detection lens are used in common is also possible.

As shown in FIG. 2A, the hologram 11
Has a grating formed in a uniform direction to diffract incident reflected light within a predetermined plane. When the grating is formed in a uniform direction in this manner, there is an advantage that the hologram 11 can be easily manufactured and cost can be reduced.

The light receiving means 20 has two light receiving portions 21 and 22 as shown in FIG.
a to 21d, and the light receiving unit 22 is divided into regions 22a to 22d.
d, and each of the regions 21a to 21d, 22a to 22
d, the photoelectric conversion signals S21a to S21d, S22a
To S22d are output.

The areas 21b to 21d and 22b to 22d form a light receiving center area, and the areas 21a and 22a form light receiving peripheral areas.

Here, the light receiving section 21 is a standard density disc L
The light receiving unit 22 is used for receiving the reflected light from the high-density disk HD. In this case, when the laser beam is condensed on the standard density disc LD having a thick transparent substrate using the objective lens 5 whose optical characteristics are optimally designed for the high density disc HD, the periphery of the laser beam is Part does not focus on the recording member surface,
Since only the central portion is in focus, the light receiving central regions 21b to 21d of the light receiving portion 21 are formed so as not to receive the peripheral portion of the reflected light, forming a central light receiving region.

By the way, when the light is diffracted, ± n-order light (n =
0, ± 1, ± 2 ...), and the 0th-order light does not change the optical path, but the + 1st-order light, + 2nd-order light, etc., and the -1st-order light, -2nd-order light, etc. are the 0th-order light. The light is diffracted in the opposite direction across the light, and the light intensity of the diffracted light of the same order becomes the same.

Therefore, a light receiving section 21 for receiving the reflected light from the standard density disk LD is disposed in the optical path on the + order light side (the left side in FIG. 2B). The light receiving section 22 for receiving the reflected light from the high-density disk HD is disposed in the optical path on the minus order light side (the right side in FIG. 2B), and this is referred to as the negative order light receiving section 22. .

As described above, the diffraction angle varies depending on the order, and the light intensity decreases as the order increases. Therefore,
In the present embodiment, the positive and negative order light receiving sections 21 and 22 are provided so as to be able to receive ± 1st order light. However, the present invention is not limited to this, and it is noted that the light may be, for example, ± second order light, and may not have the same order.

The optical axes of the −order light, the 0th order light, and the + order light exist on one plane, and the plane is perpendicular to the grating direction formed on the hologram 11.

The operation will be described based on the above configuration. The laser light emitted from the laser generating means 1 is converged into substantially parallel light by the collimating lens 2, passes through the beam splitter 3, enters the objective lens 5, is condensed by the objective lens 5, and irradiates the disk. You.

The laser beam irradiated on the disk in this manner is reflected by the recording member, condensed by the objective lens 5, and enters the beam splitter 3. Then, the optical path is changed by the beam splitter 3 in the direction of the detection lens 10, and the optical path is separated.

Thereafter, the reflected light is converged by the detection lens 10 and is incident on the hologram 11 to be diffracted. The + 1st-order light is received by the positive-order light receiving section 21, and the -1st-order light is received by the negative light. The light is received by the order light receiving unit 22.

The disk is a standard density disk LD.
In the case of, the focus signal Fo, the tracking signal Tr, and the reproduction signal Rf are calculated based on the signal from the positive-order light receiving unit 21 as follows: Fo = S21a-k (S21b + S21c + S21d) k: Constant Tr = (S21c-S21d) Rf = (S21b + S21c + S21d) ) Obtained according to the calculation formula.

On the other hand, when the disc is a high-density disc HD, the focus signal Fo, the tracking signal Tr, and the reproduction signal Rf are converted to Fo = S22a−k ′ (S22b + S22c + S22d) k based on the signal from the negative-order light receiving unit 22. ': Constant Tr = (S22c-S22d) Rf = (S22a + S22b + S22c + S22d)

As can be seen from the above equation, only the method of calculating the reproduction signal Rf differs between the standard density disk LD and the high density disk HD. That is, the high density disk H
In the case of D, the reproduction signal Rf is applied to all the areas 22a to 22a.
Although the calculation is performed based on the photoelectric conversion signal from d, in the case of the standard density disk LD, the calculation is performed based on the photoelectric conversion signal from the central light receiving area including the areas 21b to 21d.

Since the reflected light received in the area 21a corresponds to the peripheral portion where the influence of the spherical aberration is large, the signal of the area 21a is not used for the detection of the reproduction signal Rf. It is possible to obtain a small and high quality reproduced signal Rf. Therefore, even when the optical characteristics of the objective lens 5 are optimally designed for the high-density disk HD, a high-quality reproduction signal Rf can be obtained for the standard-density disk LD.

In the above description, it is assumed that at least the central portion of the reflected light from the standard density disk LD, which is less affected by spherical aberration, has a circular shape, and the light receiving center area, the light receiving peripheral area, The shape of the central light receiving area and the like has been described as an example.

However, the present invention is not limited to such a shape. Basically, it is only necessary to separate the peripheral portion where the influence of the spherical aberration is large and the central portion where the influence of the spherical aberration is small. The present invention is applicable even when the small central portion has a shape other than the circular shape, or when the shape can be approximated to a shape other than the circular shape.

For example, as shown in FIG. 3, when the central part where the influence of the spherical aberration is small is a shape other than a circle such as a quadrangle, a polygon, an ellipse, or can be approximated to these shapes from a practical viewpoint. It is possible to use light receiving means having a central light receiving area or the like corresponding to the shape.

FIG. 3 (a) shows the light receiving means 30, 33, 36 in the case where the light receiving central area is square, FIG. 3 (c) is in the case of elliptical shape, and FIG. 3 (b) is in the case of polygonal. I have. Although FIG. 3C shows a hexagon as an example of a polygon, it is needless to say that the polygon is not limited to the hexagon.

Each of the light receiving sections 31 is divided into the areas 31a to 31.
The light receiving portion 32 is divided into regions 32a to 22d and forms a negative order light receiving portion. The light receiving portion 32 is divided into regions 32a to 22d and forms a negative order light receiving portion. Is used for receiving reflected light. Further, the regions 31b to 31d form a central light receiving region.

The photoelectric conversion signals S31a to S31d and S32a to S32 are output from the respective areas 31a to 31d and 32a to 32d.
32d is output, and the focus signal Fo, the tracking signal Tr, and the reproduction signal Rf are calculated by the method described with reference to FIG. The same applies to the light receiving means 33 and 36.

Further, in FIG.
Although the case where the character is divided into three is shown, the present invention is not limited to such a dividing method.

The division method is determined by the method of detecting the reproduction signal and the servo signal. If the central light receiving area is formed so as not to receive the peripheral part where the spherical aberration is large,
The operation and effect of the present invention can be obtained.

Therefore, as shown in FIG. 4, it may be divided into right and left. When such a division method is used, there is an advantage that the track signal Tr can be detected by the phase difference method and its amplitude can be increased.

Further, the light receiving center area and the light receiving peripheral area in the positive and negative order light receiving sections need not be the same size or the same shape. For example, as shown in FIG. The light receiving center regions in the portions may have different sizes, and as shown in FIG. 4C, the shapes may be different. Further, as shown in FIG. 4D, the method of dividing the positive and negative order light receiving units may be different.

The positive and negative order light receiving portions 41 and 42 of the light receiving means 40 shown in FIG. 4A are each divided into two parts on the left and right sides. The positive order light receiving portion 41 is divided into regions 41a to 41c and has standard density. The negative-order light receiving section 41 is used to receive reflected light from the high-density disk HD, and is used to receive reflected light from the disk LD. The photoelectric conversion signals S41a to S41c and S42a to S42c are output from the areas 41a to 41c and 42a to 42c. The central light receiving areas are the areas 41b and 41c.
It consists of.

In the case of such a configuration, the reproduction signal Rf is obtained from an arithmetic expression of Rf = S41b + S41c (for a standard density disc) Rf = S42a + S42b + S42c (for a high density disc), and the focus signal Fo is obtained by using the beam size method. Fo = S41a−k (S41b + S41c) k is an integer (for a standard density disc) Fo = S42a−k ′ (S42b + S42c) k ′ is an integer (for a high density disc), and the tracking signal Tr is , Tr = S41b-S41c (for a standard density disc) and Tr = S42b-S42c (for a high density disc) using the push-pull method. FIG. 4 (b), (c)
Can be similarly defined to detect each signal.

In FIG. 4D, the periphery of the light receiving center regions 51b and 51c of the negative order light receiving portion 51 is a region 51a.
And an area 51d. However, there is no essential reason that the periphery of the light receiving center regions 51b and 51c must be divided into two. However, as described later, the tracking signal Tr in the high-density disk HD is also used by using signals from the regions 51a and 51d. Therefore, there is an advantage that the signal amplitude of the tracking signal Tr can be increased.

In the case of such a configuration, the reproduction signal Rf is obtained from the arithmetic expression of Rf = S50b + S50c (for a standard density disc) Rf = S51a + S51b + S51c + S51d or Rf = S51a + S51b (for a high density disc), and the focus signal Fo is a beam. Using the size method, Fo = S50a-k (S50b + S50c) k is an integer (in the case of a standard density disk) Fo = (S51a + S51d)-(S51b + S51c) (in the case of a high-density disk) Tr = S50b-S50c (for a standard density disc) Tr = (S51a + S51b)-(S51c-S51d) (for a high density disc) using the push-pull method.

Further, the shape of the light receiving surrounding area is not limited to a rectangular shape. That is, any size can be used as long as the reflected light to be received can be received. However, as shown in FIG. 7, which will be described later, it is needless to mention that the case where the outer peripheral shape of the light receiving surrounding area is positively used is excluded.

In the above description, the case where the optical path of the laser beam is separated by the beam splitter has been described.
The present invention is not limited to this, and the optical path may be separated using the diffraction characteristics of the hologram as shown in FIG.

The optical pickup device shown in FIG.
A laser unit 6 in which a semiconductor laser device for emitting laser light and a light receiving means for receiving incident laser light are housed in one can 6, a collimating lens 2 for converging the laser light into substantially parallel light, and a high-density disk HD. On the other hand, the optical characteristics are optimally designed, and the objective lens 5 for condensing the incident laser light is provided in the laser emission window of the laser unit 6 to diffract the reflected light from the disk converged by the collimating lens 2. It has a hologram 11 and the like.

As shown in FIG. 5 (b), the laser unit 6 includes a laser element 7 for emitting laser light, a light receiving means 20 for receiving reflected light, and a transparent unit provided in a laser emission window of a can housing these. It has a plate 9 and the like.

The transparent plate 9 is provided for sealing the can and for protecting the laser element 7 and the light receiving means 20 housed in the can. Therefore, if the hologram 11 is fixed in close contact with the can, the transparent plate 9 is not always necessary.
That is, the transparent plate 9 can be replaced by the hologram 11.

Under the above configuration, the laser light emitted from the laser element 7 passes through the hologram 11 and is converged by the collimator lens 2 into substantially parallel light. Thereafter, the laser light is focused by the objective lens 5 and is focused on the recording member surface of the disk.

The laser light reflected from the recording member is condensed by the objective lens 5, becomes substantially parallel light, is incident on the collimator lens 2, is converged, and is incident on the hologram 11. Then, the light is diffracted by the hologram 11 to separate the optical path, is received by the light receiving means 20, and a reproduced signal or the like is detected by the above-described arithmetic processing. With the above configuration, the size of the pickup device can be reduced in addition to the effects described above.

The above-described configuration is basically intended to cope with a standard density disk LD and a high density disk HD having different transparent substrate thicknesses by one laser source. However, as shown in FIG. It is also possible to use laser light having a wavelength corresponding to the substrate thickness of each disk by a laser generating means using a source.

If the hologram 11 is provided with a polarization characteristic (that is, a polarization hologram), the utilization efficiency of the laser beam can be improved.

The laser generating means 90 shown in FIG. 6 is a laser element 9 used as a laser source for a high density disc HD.
1, Laser element 9 used exclusively for standard density disk LD
2, a light receiving unit 93 for receiving a laser beam incident from the outside,
It has a can 94 for accommodating them, a transparent plate 95 provided in a laser beam emission window of the can 94, and the like.

First, the laser beam is emitted by the hologram 11
It has been described that the diffracted light is diffracted into ± nth-order light, and the + side diffracted light and the − side diffracted light are diffracted in opposite directions around the 0th order light. The diffraction angle at this time also depends on the wavelength of the laser light.

That is, even with the same + 1st order light, the diffraction angle differs due to the relationship between the spacing between the gratings formed on the hologram 11 and the wavelength. Since the wavelength of the laser beam for the standard density disk LD is longer than the wavelength of the laser beam for the high density disk HD, the diffraction angle of the laser beam for the standard density disk LD is equal to the diffraction angle of the laser beam for the high density disk HD. It is smaller than that. Therefore, in the present invention, the grating is formed corresponding to the wavelength of the laser beam for the standard density disk LD. Thus, the intervals between the positive and negative order light receiving sections can be widened, and the light receiving means can be easily manufactured.

The structure of the light receiving means is not limited to the above-described structure, but may be one shown in FIG. The light receiving means 23 shown in the figure comprises two light receiving portions 24 and 25. The light receiving portion 24 forms a positive order light receiving portion and is divided into regions 24a to 24f, and the light receiving portion 25 forms a negative order light receiving portion. Area 2
5a and 25b.

The regions 24a, 24c, 24d and the region 25a form a light receiving peripheral region.
e, 24f and the area 25b form a central light receiving area, and the areas 24b, 24e, 24f form a central light receiving area.

The minus-order light, the zero-order light, and the plus-order light exist on one plane, and the plane is a direction perpendicular to the grating direction formed on the hologram 11. Are provided so as to be parallel to this plane.

Thus, each of the regions 24a to 24f, 25
photoelectric conversion signals S24a to S2 output from a and 25b
4f, S25a, and S25b, the reproduction signal Rf is calculated by the following equation: Rf = S25b (for a standard density disc) Rf = S25a + S25b (for a high density disc), and the tracking signal Tr is calculated by the push-pull method or the phase difference method. = S24e-S24f or Tr = (S24c + S24e)-(S24d + S24f) (for a standard density disc) Tr = (S24c + S24e)-(S24d + S24f) (for a high density disc) The focus signal Fo is a double beam size method. Fo = (S24a + S24c + S24d + S25b) − (S24b + S24e + S24f + S25a) (for standard density and high density discs).

As a result, since the peripheral portion of the reflected light is not used in the calculation of the reproduction signal Rf for the standard density disk LD, it is possible to obtain a high-quality reproduction signal which is less affected by spherical aberration. In addition, since the objective lens 5 is optimally designed for the high-density disk HD, it is not necessary to remove the peripheral portion of the reflected light.

Since the disk rotates at a high speed,
The light intensity change of the reflected light corresponding to the presence or absence of the mark also changes at a high speed. Therefore, unless the light receiving means for receiving the reflected light has high frequency characteristics, it cannot output the photoelectric conversion signal in accordance with the change in the light intensity. Therefore,
Generally, an expensive light receiving element having high frequency characteristics is used as the light receiving means. However, the light receiving means according to the present invention has an advantage that the light receiving means can be manufactured at a low cost since at least only the negative-order light receiving section in which the central light receiving area is formed has high-frequency characteristics.

Further, even if the light receiving means is mounted at a position where it can correctly receive the diffracted light, the oscillation characteristics of the laser element may change due to a change in the temperature of the environment, and the wavelength of the emitted laser light may change. When the wavelength of the laser light changes, the diffraction angle changes as described above, and depending on the situation, the diffracted light may deviate from the light receiving area.

In order to prevent such inconvenience, it is desirable that the light receiving means be configured as shown in FIG. FIG.
The light receiving means 26 shown in FIG.
And positive and negative order light receiving sections 27 and 28, in which a dividing line is formed in a direction orthogonal to the grating direction to form regions 27a to 27d and regions 28a to 28d. And the areas 27a to 27d
Corresponds to the central light receiving section. Areas 27a to 27d,
From 28a to 28d, photoelectric conversion signals S27a to S27
d and S28a to S28d are output.

The positive and negative order light receiving portions 27 and 28 are formed to have different sizes. However, the light receiving portions 27 and 28 have a large influence on the reflected light from the standard density disk LD due to its spherical aberration. This is to prevent the light from being received, and to receive the reflected light from the high-density disk HD in both the peripheral portion and the central portion.

With such a configuration, the photoelectric conversion signals S27a to S27f, S28a, S2
8b, the reproduction signal Rf is calculated by the following equation: Rf = s27a + S27b + s27c + S27d (for a standard density disc) Rf = s28a + S28b + s28c + S28d (for a high-density disc) Tr = (S28a + S28b)-(S28c + S28d) (in the case of a high-density disc) Further, the focus signal Fo is calculated as Fo = (S27a + S27d)-(S27b + S27c) (in the case of a standard density disc) Fo = (S28a + S28d) )-(S28b + S28c) (in the case of a high-density disc).

Accordingly, even if the wavelength of the laser beam fluctuates and the diffraction angle changes, the diffracted light moves parallel to the dividing line.
If the movement amount is at least the area 27a, 27d, 28a,
If the distance is within the range of 28d, the diffracted light will not deviate from the light receiving area, and the reliability will be improved. Also,
In the case of the standard density disc LD, since the peripheral portion of the reflected light is not used for the reproduction signal Rf, the tracking signal Tr, and the focus signal Fo, it is possible to obtain a high-quality signal with little influence of spherical aberration. .

The light receiving means described so far utilizes the diffraction effect of the hologram. However, the present invention is not limited to these.

That is, as shown in FIG.
A configuration in which a hologram is not used may be formed by dividing into a plurality of substantially concentric circles and further dividing the upper and lower portions into two to form regions 29a to 29f. In this case, the area 29
The area constituted by c and the area 29d forms the central light receiving area.

Then, based on the photoelectrically converted signals S29a to S29b from the areas 29a to 29f, the reproduced signal Rf is calculated by the following equation: Rf = S29c + S29d (for a standard density disc) Rf = S29a + S29b + S29c + S29d + S29e + S29f (for a high density disc) Tr is calculated by the push-pull method or the phase difference method, Tr = S29c-S29d (for a standard density disc) Tr = (S29b + S29c)-(S29d + S29e) (for a high density disc), and the focus signal F is calculated according to the beam size method.
o can be obtained by the calculation of Fo = S29b-S29c (for a standard density disc) and Fo = S29a- (S29b + S29c) (for a high density disc).

Therefore, the peripheral portion of the reflected light is not used in the calculation of the reproduction signal Rf, so that a high-quality reproduction signal less affected by spherical aberration can be obtained. Since the objective lens is optimally designed for the high-density disk HD,
There is no need to remove the periphery of the reflected light.

In the above description, the light receiving means 20 having a central light receiving area and the like are used to reduce the influence of the peripheral part of the reflected light having a large spherical aberration. At this time, if the optical axis of the objective lens 5 and the optical axis of the laser beam incident on the objective lens 5 are displaced by tracking, a part of the peripheral portion having large spherical aberration in the reflected light is received by the central light receiving region. Cases arise.

Therefore, the optical axis shift can be prevented by the configuration shown in FIG. 10 so that the peripheral portion of the reflected light having large spherical aberration is not received by the central light receiving area.

The optical pickup device shown in FIG. 10 comprises a fixed optical system 101 composed of a semiconductor laser and light receiving means, a fixed deflection mirror 102 whose position is immovable similarly to the fixed optical system, and a fixed deflection of laser light. A movable deflecting mirror 103 for deflecting in the direction of the mirror 102, an objective lens 5 for condensing laser light, a lens holder 105 to which the movable deflecting mirror 103 and the objective lens 5 are fixed, a lens support 106 for supporting the lens holder 105, and the like. have.

In FIG. 10, the focus direction is F
and the tracking direction is indicated by Trd.
Is performed by moving the lens holder 105.

Since the movable deflecting mirror 103 is fixed to the lens holder 105, when the movable deflecting mirror 103 moves by tracking, the laser beam is deflected by the movable deflecting mirror 103 and enters the fixed deflecting mirror 102. The point moves by the same amount as the movement amount of the lens holder 105.

Since the objective lens 5 is fixed to the lens holder 105, the optical axis of the laser beam incident on the objective lens 105 does not shift from the optical axis of the objective lens 5 after all.

In the above description, the fixed deflection mirror 102
Although the case where is not fixed to the lens holder 105 has been described, the present invention is not limited to this, and may be fixed.

[0105]

According to the first aspect of the present invention, the center for receiving only the central portion where the influence of the spherical aberration on the reflected light from the information recording medium for which the optical characteristics of the objective lens is not optimally designed for the light receiving means is small is small. Since the light receiving area is provided, even when the optical characteristics of the objective lens are optimally designed for one information recording medium, spherical aberration occurs when light reflected from the other information recording medium is received. The central light receiving area can receive only the reflected light other than the peripheral part, which is greatly affected by the influence of light, so that compatibility with information recording media with different substrate thicknesses can be maintained and the quality of reproduced signals etc. can be improved. Become.

According to the second aspect of the invention, the reflected light is diffracted by the diffracting means as ± n-order (n = 0, 1,...) Diffracted light, and the + order diffracted light and the − order diffracted light are diffracted. Since the light is diffracted in the opposite direction with respect to the 0th order light, a light receiving means is constituted by a positive order light receiving section for receiving the + order diffracted light and a negative order light receiving section for receiving the − order diffracted light. For example, the positive order light receiving portion receives the diffracted light in the reflected light from the information recording medium having a small substrate thickness, and receives the diffracted light in the negative order light receiving portion from the information recording medium having a thick substrate thickness. Then, the central light receiving area is formed in the negative order light receiving section, so that the objective lens is optimally designed for one of the information recording media having different substrate thicknesses, so that the reflected light from the other information recording medium is The case where the influence of spherical aberration is included in the periphery Also, it becomes possible to receive only little influence reflected light from the spherical aberration, so to improve quality such as reproduction signals.

In particular, since the diffraction means is formed by forming a grating in a uniform direction, the diffraction means can be easily and inexpensively manufactured, and the cost can be reduced.

According to the third aspect of the present invention, the light receiving central regions are formed at the center portions of the positive and negative order light receiving portions, one of which forms a central light receiving region and two light receiving regions. Since at least one of the central regions is divided into two, the optical characteristics of the objective lens are optimally designed for one of the information recording media having different substrate thicknesses. Even when the influence of the light is included, it is possible to receive only the reflected light having a small influence of the spherical aberration, to obtain a high-quality reproduction signal and the like, and to obtain the divided light receiving center. The tracking signal can be detected based on the difference of the photoelectric conversion signal from the area.

According to the fourth aspect of the present invention, the light receiving central regions are formed at the center portions of the positive and negative order light receiving portions, one of which forms a central light receiving region and two light receiving regions. At least one of the central regions is divided into two, and one of them is further divided into two in the direction perpendicular to the direction of the division, so that the objective lens can optimize the optical characteristics for one of the information recording media having different substrate thicknesses. Due to the design, even when the peripheral portion of the reflected light from the other information recording medium includes the influence of spherical aberration, it is possible to receive only the reflected light that is less affected by the spherical aberration. A high-quality light receiving signal and the like can be obtained, and a tracking signal can be detected based on a difference between photoelectric conversion signals from the further divided area.

According to the fifth aspect of the present invention, when a reproduced signal is detected from a diffracted light in a reflected light from an information recording medium in which an optical characteristic of an objective lens is optimally designed, a central light receiving area and the central light receiving area are detected. When detecting with the photoelectric conversion signal from the light receiving surrounding area formed around the area and detecting the reproduction signal from the diffracted light in the reflected light from the information recording medium for which the optical characteristics of the objective lens are not optimally designed , The reproduced signal is detected only from the positive or negative order light receiving portion in which the central light receiving area is formed, by detecting the photoelectric conversion signal from the central light receiving area. Even when optimally designed for the recording medium, when the reflected light from the other information recording medium is received, only the reflected light except for the peripheral part where the influence of spherical aberration is large is Can be received by the optical area, also comes to improving the quality of the reproduced signal or the like with maintained compatibility for different information recording medium of the substrate thickness.

Further, since the reproduction signal is obtained only by the photoelectric conversion signal from the positive or negative order light receiving portion in which the central light receiving region is formed, one of the positive and negative order light receiving portions has a high frequency characteristic. And cost reduction is possible.

According to the sixth aspect of the present invention, the light receiving center regions are formed at the center portions of the positive and negative order light receiving portions, respectively, one of which forms a central light receiving region, and these two light receiving centers are formed. By dividing the area in the grating direction,
The central light receiving area, which forms the central light receiving area, receives only the central portion where the influence of spherical aberration on the reflected light from the information recording medium for which the optical characteristics of the objective lens is not optimally designed is small, and the other light receiving central area is the objective light receiving area. Since all the reflected light from the information recording medium with the optimally designed optical characteristics of the lens is received, even if the optical characteristic of the objective lens is optimally designed for one information recording medium, When receiving the reflected light from the information recording medium, the central light receiving area can receive only the reflected light except for the peripheral part where the influence of the spherical aberration is large. Compatibility can be maintained, and the quality of a reproduced signal and the like can be improved.

Further, since the light receiving center region is divided in the grating direction, even if the diffraction angle changes due to a change in the wavelength of the laser light emitted from the laser generating means due to a temperature change, the light receiving region does not deviate from the light receiving region. And reliability is improved.

According to the invention according to claim 7, the light receiving peripheral area is formed double around the central light receiving area, and
When the reproduction signal is detected from the diffracted light in the reflected light from the information recording medium in which the optical characteristics of the objective lens are optimally divided by dividing the central light receiving area and the two surrounding light receiving areas into two, the two surrounding lights are used. When detecting the reproduction signal from the photoelectric conversion signal from the light receiving area and the central light receiving area, and detecting the reproduction signal from the diffracted light in the reflected light from the information recording medium for which the optical characteristics of the objective lens are not optimally designed, the central light Since the detection is performed based on the photoelectric conversion signal from the light receiving area, even if the optical characteristics of the objective lens are optimally designed for one information recording medium, reflected light from the other information recording medium is received. In this case, only the reflected light other than the peripheral part, which is greatly affected by spherical aberration, can be received by the central light receiving area, so that compatibility can be maintained with information recording media having different substrate thicknesses and the compatibility can be maintained. The quality of the signal or the like is improved.

According to the eighth aspect of the present invention, since the laser generating means and the light receiving means are housed in one can, the apparatus can be made compact.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical system in an optical pickup device applied to the description of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a diffraction unit and a light receiving unit.

FIG. 3 is a diagram showing another configuration of the light receiving unit.

FIG. 4 is a diagram showing another configuration of the light receiving means.

FIG. 5 is a schematic configuration diagram of another example of the optical system in the optical pickup device applied to the description of the embodiment of the invention.

FIG. 6 is a cross-sectional view showing a configuration of a laser generating unit in which two semiconductor laser elements are housed.

FIG. 7 is a diagram showing another configuration of the light receiving unit.

FIG. 8 is a diagram showing another configuration of the light receiving unit.

FIG. 9 is a diagram showing another configuration of the light receiving unit.

FIG. 10 is a diagram showing a configuration for preventing an optical axis shift of an objective lens.

FIG. 11 is a diagram illustrating light-collecting characteristics depending on the difference in the thickness of a transparent substrate.

FIG. 12 is a diagram for explaining an effect obtained by shielding a peripheral portion of reflected light.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser generation means 2 Collimating lens 3 Beam splitter 5 Objective lens 6 Laser unit 11 Hologram 20,23,26,29,30,33,36,40,4
3,46,49 Light receiving means

Claims (8)

[Claims] 1. A laser generating means for emitting a laser beam to an information recording medium having a transparent substrate with a different substrate thickness, and an optical characteristic which is optimally designed for at least one of the information recording media to collect an incident laser beam. In an optical pickup device having an objective lens that emits light and light receiving means that receives reflected light from the information recording medium and outputs a reproduction signal and a servo signal, the light receiving means optimizes the optical characteristics of the objective lens. An optical pickup device having a central light receiving area for receiving a central portion where the influence of spherical aberration on reflected light from the information recording medium that is not reflected is small. 2. A light receiving means, wherein a grating is formed uniformly, and diffracting means for diffracting incident reflected light as ± n-order (n = 0, 1,...) Diffracted lights at different angles. Has a positive-order light-receiving portion for receiving the + -order diffracted light by the diffractive means, and a negative-order light-receiving portion for receiving the negative-order diffracted light, and a direction orthogonal to a grating direction formed on the diffractive means. 2. The optical pickup device according to claim 1, wherein the central light receiving region is formed in one of the positive and negative order light receiving portions. 3. A light receiving center region is formed at a substantially central portion of each of the positive and negative order light receiving portions, one of which forms the central light receiving region and at least one of the two light receiving central regions. 3. The optical pickup device according to claim 2, wherein one is divided into two. 4. A light receiving center region is formed at a substantially central portion of each of the positive and negative order light receiving portions, one of which forms the central light receiving region and the two light receiving central regions form a central light receiving region. At least one is divided into two, and one of the two is
3. The optical pickup device according to claim 2, wherein the optical pickup device is further divided into two in a direction perpendicular to the divided direction. 5. A light receiving peripheral area is formed around the central light receiving area, and when a reproduction signal is detected from diffracted light in reflected light from the information recording medium, the optical characteristics of the objective lens being optimally designed. , Detection by a photoelectric conversion signal from the central light receiving area and the light receiving surrounding area, and detection of a reproduction signal from diffracted light in reflected light from the information recording medium for which the optical characteristics of the objective lens are not optimally designed. 5. The method according to claim 2, wherein the detecting is performed only by a photoelectric conversion signal from the central light receiving area.
The optical pickup device according to claim 1. 6. A light receiving center region is formed at a substantially central portion of each of the positive and negative order light receiving portions, one of which forms the central light receiving region, and these two light receiving central regions are arranged in the grating direction. 3. The optical pickup device according to claim 2, wherein the optical pickup device is divided. 7. A double light receiving peripheral area is formed around the central light receiving area, and the central light receiving area and the two peripheral light receiving areas are divided into two. The optical pickup device according to claim 1. 8. The optical pickup device according to claim 1, wherein said laser generating means and said light receiving means are unitized.